Chapter 4 Electrical Prints, Specifi cations, and Codes 55 Copyright Goodheart-Willcox Co., Inc. (B) Corrosive Environments. (1) Galvanized Steel, Stainless Steel, and Red Brass RMC, Elbows, Couplings, and Fittings. Galvanized steel, stainless steel, and red brass RMC elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection approved for the condition. (2) Supplementary Protection of Aluminum RMC. Aluminum RMC shall be provided with approved supplementary corrosion protection where encased in concrete or in direct contact with the earth. (C) Cinder Fill. Galvanized steel, stainless steel, and red brass RMC shall be permitted to be installed in or under cinder fill where subject to permanent moisture where protected on all sides by a layer of non cinder concrete not less than 50 mm (2 in.) thick where the conduit is not less than 450 mm (18 in.) under the fill or where protected by corrosion protec- tion approved for the condition. (D) Wet Locations. All supports, bolts, straps, screws, and so forth, shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant materials. Informational Note: See 300.6 for protection against corrosion. Severe Physical Damage. RMC shall be permitted to be installed where subject to severe physical damage. 344.14 Dissimilar Metals. Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action. Stainless steel and aluminum fittings and enclosures shall be permitted to be used with galvanized steel RMC, and galvanized steel fittings and enclo- sures shall be permitted to be used with aluminum RMC where not subject to severe corrosive influences. Stainless steel rigid conduit shall only be used with the following: (1) Stainless steel fittings (2) Stainless steel boxes and enclosures (3) Steel (galvanized, painted, powder or PVC coated, and so forth) boxes and enclosures when not subject to severe corrosive influences (4) Stainless steel, nonmetallic, or approved accessories 344.20 Size. (A) Minimum. RMC smaller than metric designator 16 (trade size ½) shall not be used. Exception: For enclosing the leads of motors as permitted in 430. 245(B). (B) Maximum. RMC larger than metric designator 155 (trade size 6) shall not be used. Informational Note: See 300.1 (C) for the metric designators and trade sizes. These are for identification purposes only and do not relate to actual dimensions. 344.22 Number of Conductors. The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9. Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9. 342.56 Splices and Taps. Splices and taps shall be made in accordance with 300.15. 342.60 Grounding. IMC shall be permitted as an equipment grounding conductor. Part III. Construction Specifications 342.100 Construction. IMC shall be made of one of the follow- ing: (1) Steel, with protective coatings (2) Stainless steel 342.120 Marking. Each length shall be clearly and durably marked at least every 1.5 m (5 ft) with the letters IMC. Each length shall be marked as required in the first sentence of 110.21 (A). ARTICLE 344 Rigid Metal Conduit: Type RMC I. General 344.1 Scope. This article covers the use, installation, and construction specifications for rigid metal conduit (RMC) and associated fittings. 344.2 Definition. The definition in this section shall apply within this article and throughout the Code. Rigid Metal Conduit (RMC). A threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment ground- ing conductor when installed with its integral or associated coupling and appropriate fittings. 344.6 Listing Requirements. RMC, factory elbows and couplings, and associated fittings shall be listed. Part II. Installation 344.10 Uses Permitted. (A) Atmospheric Conditions and Occupancies. (1) Galvanized Steel, Stainless Steel, and Red Brass RMC. Galvanized steel, stainless steel, and red brass RMC shall be permitted under all atmospheric conditions and occupancies. (2) Aluminum RMC. Aluminum RMC shall be permitted to be installed where approved for the environment. Rigid alum- inum conduit encased in concrete or in direct contact with the earth shall be provided with approved supplementary corro- sion protection. (3) Ferrous Raceways and Fittings. Ferrous raceways and fittings protected from corrosion solely by enamel shall be permitted only indoors and in occupancies not subject to severe corrosive influences. Shaded text indicates a revision N(E) • • Shaded text = Revisions. Δ = Text deletions and figure/table revisions. • = Section deletions. N = New material. Part title Article title First section on the page (left page) or last section on the page (right page) Indicates new material Section title Subsection This document is NFPA 70 Part of subsection 342.56 ARTICLE 344—RIGID METAL CONDUIT: TYPE RMC 70–206 Exception Informational note Key for revision identification symbols Indicates section deleted Page number Reproduced with permission of NFPA from NFPA 70, National Electrical Code, 2020 editon. Copyright © 2019, National Fire Protection Association. For a full copy of the NFPA 70, please go to www.nfpa.org. Figure 4-17. This fi gure shows diff erent parts of the Code organization.